House_prediction.m

%whereoutputs='C:\Users\sswang\Desktop\pollcalc\pollcalc20\outputs\'; 
whereoutputs='outputs/'; 

House_history=load(HOUSE_POLLS_TXT);
d=House_history(:,2);           % julian_date
House_m=House_history(:,4);     % median_margin
House_msd=House_history(:,5);   % median_abs_dev

%%%%% Combine diffusion with a special-election-based prior 
N=DAYS_UNTIL_ELECTION
current_mm=House_m(max(find(d==max(d)))); % Find the most recent median margin
current_msd=House_msd(max(find(d==max(d)))); % Find the most recent median margin

maxdrift=4.5; % assumes modern levels of entrenchment
Mdrift=min(0.4*sqrt(N),maxdrift); % following Presidential patterns; should fill this in with House data when available
Mdrift=real(max(Mdrift,2)); % just in case something is screwy like N<0. 

% cover range of +/-4 sigma
Mrange=[current_mm-4*Mdrift:0.02:current_mm+4*Mdrift];

% What is near-term drift starting from conditions now?
nowdensity=tpdf((Mrange-current_mm)/Mdrift,3); % t-distribution is long-tailed. you never know.
nowdensity=nowdensity/sum(nowdensity);

% What was long-term prediction? (the prior)
prior=tpdf((Mrange-HOUSE_SPECIALS_PRIOR)/HOUSE_SPECIALS_SD,1); % make it really long-tailed, df=1
prior=prior/sum(prior);

% Combine to make prediction
prediction=nowdensity.*prior; % All hail Reverend Bayes
prediction=prediction/sum(prediction);

% Define mean and error bands for prediction
predictmean=sum(prediction.*Mrange)/sum(prediction)
for i=1:length(Mrange)
   cumulpredict(i)=sum(prediction(1:i));
end
Msig1lo=Mrange(min(find(cumulpredict>normcdf(-1,0,1))))
Msig1hi=Mrange(min(find(cumulpredict>normcdf(+1,0,1))))
Msig2lo=Mrange(min(find(cumulpredict>normcdf(-2,0,1))))
Msig2hi=Mrange(min(find(cumulpredict>normcdf(+2,0,1))))

bayesian_winprob=sum(prediction(find(Mrange>=0)))/sum(prediction)
drift_winprob=tcdf(current_mm/Mdrift,3) % df=3

if ~exist('whereoutputs','var')
    whereoutputs='';
end

%% write median margin prediction to csv for plotter scripts
outputs = [predictmean Msig1lo Msig1hi Msig2lo Msig2hi bayesian_winprob drift_winprob];
dlmwrite(strcat(whereoutputs,HOUSE_PREDICTIONS_CSV), outputs)